text:
How much, generally speaking, does it cost to learn how to fly?
One of my life goals is to learn how to fly a plane. I can't do it now due to time constraints, but I am curious: How much, in general terms, does it cost to learn how to fly? I.e. piloting lessons, license fees, etc. I would be doing it in the US.

Assuming a regular private pilot's license (i.e. not sport/recreation), a part 61 instructor, and a rented aircraft, then you need to budget for the following:

Aircraft rental (this usually includes oil and fuel)
Instructor time (air and ground)
Materials (books, DVDs, charts, fuel tester etc.) as recommended by your instructor
Headset
Third-class medical
Insurance
Written test fee
Examiner's fee for the actual test

If we assume the aircraft costs \$120/hr wet (i.e. including oil and fuel), an instructor costs \$40/hr and you need 50 hours to be ready for the test (40 is the minimum required) then you can do a calculation like this:

35 flying hours with instructor: \$5600
15 flying hours solo: \$1800
15 hours ground school (instructor's time): \$600
Materials: \$500
Headset: \$500
Third-class medical: \$150
Renter's insurance: \$700 (per year)
Written test fee: \$150
DPE test fee: \$400 (plus \$120 rental for the aircraft)
Total: \$10,520

You can play around with these numbers, there's a lot of variation and research is obviously important. But the single largest cost will be the number of flying hours you need, so anything you can do to reduce that time is worthwhile and the simplest - but unfortunately not the easiest - way to do it is to fly as much as possible, i.e. several times a week. Given weather and other factors, you should probably even plan to fly more than you actually can on paper: a bunch of flights will certainly be cancelled.
You can also train in the most 'minimal' aircraft you can find: a two-seater aircraft without a glass panel could be \$50/hr cheaper than a four-seater with a G1000. Unless you have a very clear idea about what sort of flying you'll do in the longer term there's no point in paying for anything that isn't directly required for the private pilot's test.

I know this is an old post but I'd just like to add that I have non-owned aircraft insurance for $160/year. The biggest variable to insurance is the amount of coverage you need. My flight school only required $5000 to cover the deductible, if you are insuring the whole aircraft value the cost can be significantly different.

The minimum required hours of instruction is 40 hours.  How many will you need to get the license?  That depends on a lot of factors.  Very few students are good enough at 40 hours to pass the practical test.
If you can only fly once per week, you will "forget" some of what you learned on the last lesson.  "Forget" is in quotes because some of the forgetting is intellectual, and some is forgetting the sight picture and muscle memory of what you should be doing.  Bottom line is that if you only fly once per week it will take longer.  It took me about 70 hours over a period of about one year, flying once per week with the usual weekends not flying for family obligations and weather.  70 hours was, back then, about the national average.
So multiply 70 hours by your flight school and CFI's combined hourly rate.  Then add some for ground schooling.

This is a great answer because it was correct 20 years ago, it's correct now, and it's likely to be correct 20 years from now.

With weather, unscheduled maintenance, family obligations etc, once/week can turn into once/month or worse.  If possible, try to plan on 3 or 4 times per week.  That way missing one doesn't hurt you so much.

The number of hours you take will depend a lot on how much time you can devote to flying and studying. I taught for several years at a college where my students were flying at least 4-5 times a week. They probably averaged 40-50 hours before their tests. Outside of college, where my students only flew a couple of times a week, they probably averaged 50-60 hours before their tests.

And a good quality, motivated (and motivating) instructor will make a HUGE difference in both the time it takes you to complete your rating and the quality of the instruction you absorb. A bad CFI will run you off from flying very quickly. Whereas a good one will pass along lessons that you'll remember for the rest of your life.

I added mine up after I finished, and it came to about \$12,000 over about 18 months.
I didn't push myself to finish as cheaply or quickly as possible.
I think I finished around 55 hours.
(I also flew out of a relatively expensive airport/region)
If cost is a major factor, you can find ways to trim some costs.
Basically, every moment you spend preparing, studying, "chair-flying", and practicing procedures on the ground is a cost that you don't need to incur in the air.
Make sure you have each procedure down solid, know your target airspeeds, altitudes, and courses, then hopefully when you get in the air, you won't have any wasted maneuvers because you forgot to setup properly.  Make every moment of actual HOBBS time count towards flying experience, and not for something that could've been covered on the ground, and you can probably trim 25% or more off the cost.

That is something I have learnt in the hard way and I am still learning it. Surely practice your lesson on the ground and know exactly what you are going to do in the air before you take off, that saves a lot of time, most of the time.

StallSpins answer is probably correct, however as you haven't flown a plane before, I suppose you don't know a lot of aircraft terminology (like VFR/IFR) either.
First of all, you should know that there are different types of licenses. The one you want to do is the PPL - a Private Pilot License. In the US this enables you to fly single-engine Planes during the day and the night in so called "VFR-Conditions", meaning that you navigate by matching a map with the terrain below you and fly a course you defined before. Obviously you cannot fly if you cannot see much of the terrain, there are some minimums like visibility in order to fly.
Also you cannot use this license for commercial actions like shipping cargo or transporting persons, if you get more money from it than it actually costs you.
Even though most schools advertise that the PPL costs 6000-9000 USD, this only includes the minimum hours (and I have been told by US flight instructors that it is not possible to actually stay within the minimum hours). I would therefore say it costs at least 10,000 to 14,000 USD, depending on how good you perform.
This is still cheaper than my European PPL, I paid about twice as much for it.

May I know in which country you got it ?

I have done my ATPL in Germany and the US

Highly depends on where you go. The big pt 141 school north of me charges \$9,000-12,000. You'll learn in IFR equipped mid-80's model 172's.
Learn with me or my partner, and you'll pay about \$6,000 if you don't waste time. We have a 172C and a 172M. They're not really IFR equipped (they are but not enough for any real IFR flying) but they're well maintained and all that. Without sacrificing safety, we keep our costs to a minimum and that's passed directly on to the student.
The big school has a good part 141 curriculum and great instructors, but the average guy wanting to learn to fly doesn't need a special course or high-tech instruments and other costly devices for training. It's far cheaper to learn with the basics and then transition into that other stuff when you need it. I can promise people they're not missing anything, because I went through a 141 college program and I'm teaching the exact same stuff, almost the same way under part 61.
Anyway, I would say to look at \$6,000-\$10,000, depending on the aircraft and your location.

where do you teach?

This would be a totally acceptable time to plug your own school! :)

I would like to congratulate StallSpin for not promoting his flight school, but simply answering the question based on his knowledge. Though, I would think that it would be OK to state where in the country you are so those in your area who may want to get in touch with you could.

I would just like to note that if your dream is just to get up in the sky and fly, there are cheaper options than the "full" PPL. I have no experience with the US LSA license but in Europe there is a similar "ultralight" category that allows you to fly small sporting aircraft with limited MTOW, but thanks to modern materials, most of these newer small planes are very advanced, comparable to bigger airplanes in many ways. Other restrictions include: a limit of only a max. of 1 or 2 persons on board; you can only fly in good weather and during daylight.
I have fulfilled my dream of flying by doing a course for ULL (ultra-light airplanes license) in Europe, which cost me about 3,000 EUR (it's hard to separate all the costs like driving to the airfield, non-essential books etc). As for the American LSA, there are many articles in the internet like this, estimating the costs at around 4,000 to 5,000 USD.
It's important to note that even once you have the license, the costs of flying are still high. But these smaller airplanes are cheaper and have cheaper operating costs (no, you definitely won't save any money, but you'll fly more for the same price).
A very different alternative are also gliders, which bring many people to flying and - once again - if you just want to fly, gliders might be perfectly "enough" (or maybe even better) for you, at a fraction of the price.
And finally - even the training flights are great. I didn't have to "suffer" through the training, I've enjoyed most of the flights, so I wouldn't separate the costs of "before" and "after" strictly.
(My opinion in this answer comes from a strictly free-time for-fun aviation point-of-view. People aiming higher probably won't agree with me.)


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Can I get a Private Pilot's License if I have controllable ADD and just send a waiver to my doctor?
Hello I am a fan of aviation and would love to be a private pilot, but I have ADD that is controllable. I can control my ADD and I'm cancelling my medications. Can I get a medical certificate if I just send a waiver from my doctor to the AME or FAA? Thanks for the help

Although you're not reapplying this question does address applying for a medical with history of ADD.

See this question and the FAA's examination requirements. Unfortunately, once you've been diagnosed with AD(H)D it becomes quite difficult to get a medical, even if you're now off meds. Ideally you should have a consultation only - don't apply for the actual medical! - with an experienced AME who's dealt with similar cases before. A sport pilot license could be another option; there's no medical required.

Your doctor cannot issue waivers, only letters concerning your treatment. Getting a waiver is done through the FAA and as Pondlife said, is very difficult even after discontinuing medication.

Yes, by going through the proper steps you might get a medical. Be sure you don't mistake "difficult" for "impossible". If you are motivated and stick with it you may very well be able to get a medical if you are no longer taking medication despite a past diagnosis.

Pond life is right, consultation only cuz if you are denied you can never go LSA, which is where you,re headed.

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What would be the designation for 4 parallel runways?
If an airport were to have 4 parallel runways (ex if KSEA added another one), what would the designations be. Would it be 34L, CL, CR, and L? I know in Orlando they are separated by the terminals, and thus quite far apart, and they're numbered 17 and 17 and 18, for example. But if they were right next to each other, would that make a difference? Would the two-number system still be used there?

I disagree with the close votes. The previous question is a very general numbering question and does nothing to get an answer for this question on a specific case.

@Robert Yes it does. This question is in fact explicitly answered there.

@voretaq7 I missed that part, apologies. Easily missed with so many long answers.

@Robert Yup, it's easy to miss - that's why I linked to it :)

Airports can have a left, center and right runways.  Memphis (KMEM) is a good example.  Airports with four or more parallel runways are left and right with the numbers off by one.  Los Angeles (KLAX) and Chicago (KORD) are good examples of such an arrangement.

Roissy Charles-de-Gaulle (LFPG) also uses the same strategy in Paris, with runways 9L/9R/8L/8R

KATL has six parallel runways

@TomMcW where? I only see 5.

@lightbord Sorry, you're right. There's only 5. I was thinking it was 6

The 6th one is a little further south. It's only used by the unicorns, though, so it's not on most charts.  :)

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On a calm day, what determines the active runway?
When the winds are "calm" or variable, and as such there is no wind direction on which to base the decision on what the active runway should be, how is that determination made?

Good question. I always imagined it was geography (which runway lines up best for incoming and outgoing flights, surrounding terrain, and possibly shortest distance to terminal), but I never actually knew.


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Does lack of a curved taxi-line indicate a turn is not permitted?
Does the lack of a curved taxiway centerline between two taxiways indicate that a turn is not permitted?
Take for example the complex of taxiway connections at KATL here: 33.636153, -84.421919 (see on google maps). At this intersection, there are several connections between taxiways that don't have a curved line between them. See the attached image for specific examples. Does this indicate that aircraft are not permitted to take this path, whether it's for operational, safety, logistical, or other reasons? If so, are there exceptions to these rules in certain circumstances?

No, lack of a centerline stripe doesn't restrict a controller from assigning that routing, nor does it restrict a pilot from turning there.
The stripe might be omitted because "that" turn wasn't anticipated to be used often, but the stripes (or lack thereof) carry no regulatory authority.

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Why would an airport use an L/R runway combination and a second number instead of L/C/R?
At KPHX, there's a Runway 25L/R and a runway 26. What would the reasoning be for using this instead of what seems to be the more common L/C/R designation?

While it is going to be very hard to pinpoint the exact reason for KPHX, there are several logical reasoning for why it is done in general (I must disagree with your observation that XL/C/R is more common than XL/R, X+/-1 configuration, especially when there are more than 3 parallel runways).

Avoiding confusion. During rush hour it might be too confusing to have 3 runways with the same number

Separate complex. There is a good 1KM (3,500 ft) between 8-26 and 7L-25R centerlines. Using a different number helps to artificially (or not so much) separate the airport to different areas (some airports literally use N/S or W/E "complex"/"area" on the official charts)

Preparation for the future. If KPHX is ever going to get a fourth parallel runway to the north of 08-26, it will be much easier to add L/R to the existing runway than renaming the supposedly 07C-25C

I think "separate complex" is most likely. Consider KATL, 26L/R north of the terminals, 27L/R south, and 28 much farther south. In both cases, "the 25's" or "the 27's"  are close together, while "the 26's" or "26" is "over there." Three moderately close parallels in the same complex, like SEA or DFW, make the case where a Center runway fits rather than disrupts a clear mental picture of things.

Airports with three runways in the same direction close to each other are probably pretty rare, because you'd need non-conflicting arrival, departure and missed approach patterns for all of them, and "center" runways would likely end up with a long corridor of airspace that all traffic needs to go through, the area used for sequencing would be far back, a missed approach would be a long detour, and emergency procedures would involve clearing the airspace of another runway. It's an operational nightmare you need a good reason for.

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can an aircraft land on an aircraft
Assuming the larger (receiving) AC has holding mounts and the smaller AC can slowly approach without contacting the tail. Possible example, land a cesna on the back of a C130
Would the weight of the smaller aircraft be compensated by the lift generated from it's wings?

Used to happen all the time with blimps.

The other question doesn't cover additional weight / additional lift.


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How do planes receive their flight plan?
When planes land, do they receive a hardline connection to ATC in order to receive the next flight plan, or do they receive their flight planes wirelessly from ATC?

Planes receive flight plans? Or their pilots do?

I'm guessing you are talking about route schedules and not "flight plans" per se.

Flight crew (pilots) receive flight clearances by one several means including by phone, radio, or electronic text. Unless a dispatcher is involved, the flight plan is not received by the flight crew; rather the flight crew gives the flight plan to ATC before receiving their clearance. If a dispatcher creates the flight plan, then the crew must get the flight plan from the company dispatcher, not from ATC.

Are you asking about airline operations? Flight plan submission and handling can be very different between airlines, charters and individual flights.

You don't "receive" a flight plan, you file a flight plans and later receive a an IFR clearance based on it.


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Where can I find EUROCONTROL's fuel coefficients for the B737?
I am trying to compare the fuel impact of different types of approaches, to compute the fuel flow I am using a model developped by Eurocontrol (Base of aircraft data). I am struggling to find the fuel coefficients necessary for the computation. Do you know where this data can be found ?
I am particularly interested in the B737 (-600,-700 and -800) and the A320, I have found this http://catsr.ite.gmu.edu/SYST660/B737_BADA.pdf which is exactly what I am looking for but I find the value of the second thrust specific fuel consumption coefficient (.10000E+15 kts) quite weird because it is very different from what I had read before. For example it's .14300E+04 kts for the B767-300 https://www.eurocontrol.int/sites/default/files/field_tabs/content/documents/sesar/bada-b763-opf.pdf and I trust this link since it comes from Eurocontrol's website.
Does anyone know whether this data is accurate ?

Why don't you write an email to Eurocontrol [the BADA team] and explain them what you are doing. Apply for a license to BADA 3.latest, sign the NDA and get the data you need.

Thank you for your answer, I have just sent them an e-mail, since it's written on their website that licenses are only available for companies I am not sure I will get an answer though


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How does the A220-300 have lower fuel capacity and longer range than the -100 variant?
The A220-100 and -300 variants have relevant specs of (respectively)

fuel capacities of 21,805L and 21,508L
MTOW of 63T and 71T
Range of 3450 nmi and 3600 nmi

How is the bigger, heavier variant specified to go further on less fuel?

The only thing I can think of is that the newer model has more efficient engines.

They both use PW1500G engines, as they were designed and tested mostly in tandem. The larger one obviously has units rated for higher thrust, but again, that should come at the cost of increased fuel burn.

I assume the numbers you found are from the Wikipedia article. If you look closely at the specifications table, you'll see that the numbers are from two different publications:

The Airbus Family Figures Booklet (2019), which lists the following data:

A220-100
A220-300

MTOW
63.1 t
69.9 t

Fuel Capacity
21 805 l
21 508 l

Range
3400 NM
3350 NM

An article (2021) about improved MTOW and range for the A220-300:

It will take the MTOW of the -300, the larger of the A220 variants, to 70.9t from the current 69.9t and will provide some 200nm additional range.

So the range of the A220-300 was originally lower than the -100, but was improved due to the higher MTOW. It still has a lower fuel capacity, but range (with payload) is not limited by fuel capacity. It is limited by MTOW as you can see in the payload/range plots:

A220-100

A220-300

As you can see from these plots, the maximum range (ferry range) of the A220-100 is higher than the -300, but the -300 can fly further with 140 passengers than the -100 with 120 passengers due to its higher MTOW, therefore giving it a higher typical range.

We wrote the same answer at the same time . I deleted mine since your is more elaborated. Shall the Wikipedia entry be corrected?

Yeah, I was going off of what specs WIkipedia lists, on the (apparently false) presumption that there are enough people really interested in details of aviation that it would be up to date and consistent. Apparently not. Thank you!


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Can stored/leased 737s be used to substitute for grounded MAXs?
The 737 MAX was introduced relatively recently. I would have assumed they were replacing at least some older 737 models in operation with the major airlines that took them (eg Southwest, American, United, in the US). Did those airlines immediately sell off their older planes as the new ones joined their fleet? I see reports of huge flight cancellations from lack of the new aircraft. Since they have common type ratings with the earlier 737, what happened to the older planes that none of them can be pulled from storage or dry leased and put back into service? Surely this grounding is long enough to be worth the transient expense?

If you have multiple questions (airlines selling old jets, consequences of regulations on other aircraft of the same type without a specific problematic device, economical consequences of ... I don't understand your last question) you should ask them separately.

It really isn't 1 new aircraft = 1 mothballed aircraft. Most of the 737 MAX aircraft were fleet expansions (for US carriers). The older aircraft get retired when they aren't economical to fly anymore, and even then a retired aircraft is often sold either to a scrap yard or to a lower budget operator. In order to bring an aircraft back into service they may have to go through C or D checks before they can be considered airworthy again (because old aircraft are often retired at a D-Check when it needs a major check).
Airlines need to schedule C/D checks out months in advance, each aircraft costing millions to go through the check and a month or more of downtime. There is only limited space available to do these checks, so even if they wanted to bring 10 aircraft back into service, it may take 6 months and cost $20-40 million. It's cheaper to cancel the flights.

It's cheaper for the airline to cancel the flights because to a first approximation all other rival airlines would undergo the same cost. Therefore each affected airline can charge the passenger (you can charge to the extend that your rivals do without worries).

The main problem is in the United States, the 737 Classics are banned beginning December 2017, due to fuel tank inerting requirements. In particular, Southwest's Classic replacement schedule was driven by this, their last flight was in October 2017. They have a number of parked Classics, but they can't be operated in the US. On the other hand, the 737NG is new enough that there isn't a significant excess fleet.
Due to the TWA Flight 800 explosion, FAA required retrofit of fuel tank inerting on most aircraft with center tanks. This system purges some center tank oxygen with nitrogen, in order to reduce the risk of explosion if there's a spark. EASA did not require retrofit, and the MD-80 is exempt (no heat sources by its tank).
While a retrofit was developed for the 737 Classic, the cost of the system, coupled with the age of the aircraft, and the 737 skin issues, meant that all the big US carriers chose to retire remaining 737 Classics as of the deadline, rather than retrofit.

Thanks. To be clear, 737 Classic are the -4/5/600 set, right?

@PhilMiller The 737 "Classic" is the 300/400/500 series.The -600/700/800/900 is the NG.


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How is the climb/descent performance affected by wind gradient?
I am exchanging opinions with other pilots concerning climbing and descending with a wind gradient, and I'm facing strong opposition... In my opinion, a plane trimmed for S&L flight, if it encounters a headwind with a positive gradient (wind getting stronger with altitude) will gain altitude, since–because of the gradient–it will harvest some of the wind energy. In other words, part of the energy of the wind will be converted in potential energy of the airplane.
When descending in a tailwind with a positive gradient, things will take place in reverse: the plane will lose altitude, since a part of the potential energy of the plane will be transferred to the moving air, resulting in an increased KE of the wind...
Is my theory correct?

You are correct.
Suppose the headwind just 10 meters above you is 10 knots stronger then where you are now. Climbing the 10 meters will cost you some kinetic energy which is transformed to potential energy. Suppose you were flying 200 knots airspeed initially, you will end up with 198.1 knots airspeed if the transformation from kinetic to potential energy is 100%.
I derived this from simple kinematic energy equations:
$\frac{1}{2}mV_0^2 + mgH_0 = \frac{1}{2}mV_1^2 + mgH_1$
$V_1 = \sqrt{V_0^2+2g(H_0-H_1)}$
But since your headwind is increased by 10 knots, your true airspeed will be 208.1 so it has increased by 8.1 knots. Free energy from the wind!
Note that your groundspeed will reduce during such a climb, but you will be able to generate a higher than usual climb rate at constant airspeed in a positive gradient headwind field.
Note that birds make use of this technique, for example the albatross can stay airborne for days with using only minimal energy for keeping in the air.
Albatross in windshear field (youtube)

I would think you would loose 10 knots ground speed for an increase in headwind 10 knots and  loose slightly less than 2 knots airspeed for the trade of 10 meters in altitude, per the rule of thumb 9feet per knot per 100knots. Interesting brain teaser.

I believe that the ground, as a reference, should be excluded from any analysis. You are flying, and the only valid reference is the mass of distant, immobile air...

We can make a 'mental experiment': you descend in a tailwind with a positive gradient. You'll find a growing tailwind, and in order not to crash, you should give gas... By so doing, you supply energy to the wind through the propeller, while descending... Now, let's think in the inverse situation: climbing with headwind in a positive gradient. It seems reasonable that things will be precisely the opposite: The wind will now supply energy to the plane, while climbing...


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Is it possible to control a drone with a link mediated by the cellular phone network?
If that were possible, it would allow an operator to control the drone from a very remote place, and without resorting to satellite radio links, as military drones do...

Sure, but depending on where you are flying, this may be illegal (like in the US).

Possible: yes
Probable: no
The simple fact is that the cell network is not advantageous for drone control at least not the kind that people prefer. The architecture of the network by nature allows the signal to drop out bandwidth from tower to tower is not guaranteed. This would allow a situation where a drone flying along would get handed off to a tower that has no available bandwidth and the control signal drops out. Dedicated satellite networks allow point to point communication as well as assured bandwidth when its needed.

In theory yes.  However the drone is going to be a bit hamstrung for several reasons.
First, it will be dependent on cell reception to operate.  This is going to restrict its operation to populated areas with good cell networks as well as restriction operations to low altitudes, say less than 2000 ft AGL.  This makes the drone of limited use for commercial or military applications.
Second either the drone would have to be designed to be cross platform compatible with multiple types of cell networks eg GSM, CDMA, etc. and would impose even more restrictions upon where the craft could be operated.
This would leave the only practical users as civilians operating local within a specific country and most are subject to restrictions such as the United States' CFR Title 14 Part 107.31, which restricts operation of small drones to flight within visual line of sight operations without special waivers.
For these reasons a cell linked UAS would effectively be impractical.


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What are the procedures for radio malfunction
I was reading this question Do airline pilots ever risk not hearing communication directed to them specifically, from traffic controllers? and there is a answer mentioning radio malfunction

If it's a real radio problem, there are procedures for both sides to follow to keep everyone safe.

How do pilots / ATC work together if radio does not work?

Possible duplicate of How would an airplane land if the on-board radio breaks down?

@Jamiec thank you; could not find the question you linked.


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Avoiding leaded gasoline in aviation
I would like to get into aviation, but I have concern about the leaded gasoline used in most small engine planes.  How difficult will it be to avoid avgas while learning to fly?  And how should I go about doing this?  In particular, is it typical for flight schools to have diesel planes available for flight instruction, and is it reasonable for me to insist on this?

This may vary a lot from region to region. Which country are you asking about?

See http://aviation.stackexchange.com/questions/7797/does-the-lead-in-fuel-harm-passengers

@J.Hougaard California.

@J.Hougaard In response to the link you provided, I am well aware that there is no lead exposure once you are airborn.  But while fueling, or if the engine is running while the plane is stationary, you are sitting in a cloud of tetraethyl lead vapor.  I take no chances with that stuff.

You're far far more likely to die from lack of 100LL than from the lead inside it. (Fuel starvation during flight)

J. Hougaard's answer is a bit of a smart @ss but it is one way to fly without using leaded fuel minus whatever is burned in the engine of the tow plane.  But there a few more alternatives as well.
Do your primary flight training in an aircraft powered by jet fuel - Jet-A does not contain lead in it so it is no more risky than unleaded automotive gasoline.  However this will dramatically increase the price of your primary flight training by doing it in a turboprop or turbo jet powered aircraft.  One 'relatively' economical alternative would be to do the primary flight training in a turbo diesel powered airplane such as diamonds DA 42 or DA 62 aircraft.  Cessna briefly introduced a version of the 182 aircraft powered by turbo diesel, and Redbird has recently introduced rebuilt versions of the 172 powered by Redhawk turbo diesel engines and equipped with new avionics. But it may be sometime before these aircraft are ubiquitous enough that you can frequently encounter them at flight schools.
Do your primary flight training in a light sport airplane. LSA's - especially Rotax powered LSAs - can be fueled by premium unleaded automobile gasoline, and many flight schools operating LSAs like this because it is a little bit more inexpensive than Avgas and eliminates lead deposits in the engines.  If you know of a flight school which uses LSA's, stop by and inquire whether they're using unleaded gasoline in their aircraft.
Wait 5 to 10 years then do your flight training. The FAA is in the process of transitioning to in unleaded avgas alternative.

Thanks for the LSA remark---that seems like the most viable option.

@Yly Note that the vast majority of light-sport aircraft burn leaded fuel simply because that is what you can obtain at most airports. I don't know what the fueling situation is in your area, but at my home field any gasoline-burning engine is fueled with 100LL because all that's available on the field is 100LL or Jet-A.

You could fly gliders. They don't use leaded fuel. In fact, they don't use fuel at all.

This is a long answer but I think it explains a viable, realistic alternative to 100LL and Jet-A.
There is a common alternative to 100LL: regular gasoline!
Many airplanes, particularly trainers, can use ethanol-free automotive fuel interchangeably with 100LL.  It's just a matter of finding a school that has the right airplanes.  All you need to do is call up your local schools and ask if they offer trainers that burn MoGas (or auto fuel, pump gas, regular gas, or any other name you can think to call fuel that you put in your car).
I have many hundreds of hours flying very high time engines (>3000hrs in some cases) that burned MoGas and can tell you that there is nothing unsafe about the fuel (I preferred it, actually).  The engines ran very well and rarely fouled like their leaded counterparts did. The next plane I own will have a Supplemental Type Certificate (STC) for MoGas.
MoGas is sourced form gas stations that sell ethanol-free fuel.  It's that simple.  A school that fuels with MoGas likely owns a dedicated fuel truck and will drive it to a gas station to top off the tanks from the pumps just as you would a car or a boat.  A tiny amount is pumped into the tanks to clear the lines of other grades, a sample of "clean" fuel is taken and tested for alcohol and, when found to be pure, the fuel truck is topped off and driven back to the flight school.
A very short list of common trainers that run on 87 octane MoGas:

Cessna 150s with O-200 engines
Cessna 172s with O-320 or C-145/O-300 engines
Cessna 182s up through the 182P
Just about any Cherokee/PA-28 can run MoGas but some of the higher power models (160hp and higher) require modification.
For multi-engine training, the venerable PA-23-150 Apache can be flown on MoGas.
Just about any other airplane with Continental A-, C-, E-, and low power O-470 engines...
Just about any Lycoming engine smaller than the O-320, except the O-235...
Even larger Lycoming and Continental engines can use MoGas in some cases!

The common low-power training airplanes (C-150, C-172, PA-28, etc.) running lower horsepower engines (O-200, O-300, O-320, etc) rarely, if ever, require any modification to run MoGas.  Planes with derated high-displacement engines, like 225hp O-470s, can also run MoGas legally without modification.
There are plenty of options for training and ownership that do not involve leaded fuel.  You can see if you are located near any known "pure gas" stations here.  The eco-folks in California seem to like ethanol so it may be hard to find ethanol-free fuel in your state.  The map is merely what is reported and is not a comprehensive catalog of MoGas locations.  Marinas can also carry alcohol free MoGas but are typically very expensive.
Edit: there are many common misconceptions floating around about MoGas.  There's nothing special about it and airplanes rarely require modification to burn it (I've never flown one that has needed a physical mod).  It's a very safe, stable, and cheap alternative to 100LL.  The flight school I work with uses MoGas religiously as did the one I worked with previously.

This is not readily available and the aviation engines mentioned require an STC kits to be fitted prior to using MoGas.  You can't run down to your local flight school and demand they fuel their airplane's with MoGas as a customer preference; that just won't work.

Well, you can ask nicely.  Most planes that qualify require no modification whatsoever.  O-320 powered Cessna 172s, for example, need only a piece of paper saying it's legal.  Same with C-150s.  Same with Cherokee 140/150.  Same Aeronca Champs and Chiefs.  Same with Apaches.  A plane with a 160hp or greater engine may require physical modification.

The "kit installation" process for most airplanes is described here: http://www.autofuelstc.com/stc_specs.phtml


text:
How do pilots identify the taxi path to the runway?
When the aircraft is readying to taxi, the ATC asks them to proceed to some runway number, say runway 09. In big airports, how do the pilots identify the correct path to their runway?
Does the ATC guide them? Or do they get a map of an airport chart?

For the media component - Everybody Loves Kennedy Steve  To follow along, Grab the Map!

Almost always pilots use a chart, ie a map which shows the airport from the air. Runways are numbered according to their magnetic bearing (runway 22 is roughly aligned to 220 degrees magnetic for example) while taxiways are lettered. As an example see the chart for La Guardia.
A pilot would be given a taxi clearance which gives an end destination and a set of taxiways to take in the order they should be taken. For example, a pilot parked near the fire station might be given a taxi clearance like "US123 taxi to runway 31 via Foxtrot, Alpha, Lima, Bravo and Zulu." The pilot would look at the map and see the paths to take.

While taxiing there are signs on the ground which assist the pilot in navigating the taxiways. Some give directions, some indicate places where ATC have to clear a crossing.

Occasionally a pilot will need additional guidance in which case they can ask for a progressive taxi, where ATC will guide them through the airport, but this is rare as it is very labor intensive for ATC. There are also vehicles with "Follow Me" signs and lights which can be sent as well (these vehicles need clearances too).
It is good practice for pilots to study the ground plan for any airport they plan to visit so they know what to expect when they get there, and have the plans available in the cockpit.

Is it good form to issue those taxi instructions without either a clearance to cross runway 4/22 or instructions to hold short of it?

Are you referring to the ILS hold line or the actual runway? The ILS hold line is not explicit so ATC must issue a hold there if one is necessary, conversely, an aircraft shall not cross RWY 4 without an issued clearance. So a taxi instruction without a RWY 4 clearance and without a hold should would be an instruction for the aircraft to cross the ILS hold line and stop at RWY 4

@hmakholm, in the USA it used to be the case that a "Taxi to" instruction was implicit clearance to cross all runways on the way to the specified runway. They got rid of that a while ago, now we only say "Runway 31, taxi via..." and all runways require an explicit "cross" instruction before pilots may cross. In addition, if it is not our intention to issue a crossing when the aircraft gets close to the runway, we have to issue an explicit "hold short" instruction.

'follow-me' cars, and progressive taxi can be used, but at a towered airport, ground control will give you that with your taxi clearance.
"United 2133, Laguardia Ground, taxi from the commercial ramp to runway four using taxiway alpha, echo, and bravo."
Using a taxiway diagram from the A/FD, you would locate your position on the plate, the taxiways in question and from there determine the route you will take.  In this case you'll turn left from the ramp heading northwest on taxiway A, then take a right on taxiway E, then take a left on taxiway B.

If you are unfamiliar with the airport, you can then request a progressive taxi."
"LaGuardia Ground, Beech 2375 X-Ray, Unfamiliar with the airport layout. Request progressive taxi."
NOTE: This will annoy controllers at busy airports if you habitually do this as it is expected that you have this information ready at hand before you call ground requesting a taxi clearance.
The 'follow me' vehicles are usually used for quickly routing VIP or special use aircraft to a section of the ramp e.g. Trump's 757 to a section of the ramp cordoned off for a campaign rally, etc.

Very often, the instruction is in the form "Taxi to holding point RWY 24 via H, L, cross RWY 13, K, B." The letters are the names of the taxiways.
The pilot then looks into the airport chart and follows exactly as instructed. You must hold short before crossing runways, unless they are used as taxiways.
It is easier when the instruction is followed by "Follow the follow-me car.", then you just follow the car.

They have the charts in the cockpit, either in electronic or in printed format.
As an example, see page 83 of this pdf, showing the charts for Amsterdam's airport (AMS/EHAM).
ATC will not only tell them to which runway to go, but also which taxiway(s) to use to go there.

In pilot training, it is taught to have a diagram of the airport and to study it before flight.
The tower is usually willing and able to help (as described in other answers: progressive taxi) but depending what airport you're at, you may have to act like the pilot in command and know what ATC is talking about. You'd need to know where to taxi and you'd need to do it fast.
Having the diagram of the airport is necessary but you also need to know it.  Sometimes taxi instructions change midway through taxiing.  You get the point.
The bottom line: pilot in command has to know where and when to taxi.  The rest of it is nice-to-haves.


text:
Did any aircraft ever use stick twist for rudder control?
Did any aircraft ever use stick twist for rudder control like some joysticks for video game flight simulators?

Simmers soon use rudder pedals to get the possibility of differential braking.

@mins A real aircraft recently used stick twist for rudders.  See my answer, below. :-)

Yes, the RAH-66 Comanche FBW system used a twist control for the yaw channel.
The RAH-66 Comanche used a twist in the pilot's stick to control the rudder/yaw inputs.  It had no rudder pedals.  (Yes, a helicopter is an aircraft).
Comanche unfortunately was canceled near the end of LRIP (Low Rate Initial Production) in 2004 as the program was moving into EMD (Engineering and Manufacturing Development). There were at least 2 prototypes flying at the time. Test and development flights took place from 1996 to 2004.
Extracts:

"... the RAH-66 Comanche design incorporated a 3-axis, limited displacement, uniquetrim sidearm controller [replacing cyclic and yaw pedals] for control of the longitudinal, lateral, and yaw axes. A proportional collective with approximately 6 inches of displacement was used. An enhancement tailored to the scout mission was the incorporation of limited control in the vertical (fourth) axis of the sidearm controller. This allowed the pilot to command stabilized climbs and descents with the altitude hold system engaged. This was used primarily for vertical unmask and remask maneuvers, which enabled the pilot to fly through the autopilot without even temporary disengagement."
— "Impossible To Resist" - The Development Of Rotorcraft Fly-By-Wire Technology (PDF—Paywall)

and

"The RAH-66 Comanche program has proposed 4-axis controller (Harvey, 1992), but this approach is now questionable."
— A Four-Axis Hand Controller For Helicopter Flight Control

(Source)

Note that either the '3 + 1' or '4 + 1' controller configuration would likely have been the ones decided on for the Comanche, on the basis that all the cockpit pictures that have been seen feature a sidestick and a collective stick, but no pedals.

As noted in the first text block (Impossible to Resist) the 3+1 (collective) was the final form, although the cyclic had some control authority in the vertical axis (as described). I added the emphasis in bold, and the note on "side arm controller" vs "cyclic" in brackets.

@ymb1 No, I don't mind, thanks.

If you want to include radio-controlled model airplanes as "aircraft", then the answer is that yes, there have been some single-stick transmitters that use twisting of the stick to control the rudder channel.


text:
What is formula for induced drag in stalling regime?
I'm wondering what is the formula for induced drag in a stalled regime, i.e. in a regime where the $C_L$ (coef. of. lift) has started to decrease but is still nonzero.
I've a feeling that the conventional formula for induced drag
$$D_i = \frac{L^2}{\frac{1}{2}\rho V^2   \pi b^2 \epsilon}$$ (taken e.g. from this answer) which in essence depends on lift $L$, does not explain induced drag in stalling regime (if it would, it would erroneously imply that the induced drag is equal for a pair of AoAs $\alpha_{\text{before-stall}} < \alpha_{\text{after-stall}}$ which both correspond to the the same $C_L$).
I've come across the evidence that induced drag continues to grow as square of AoA even in stalled regime (e.g. schematic Fig. 4.14 from av8n.com)

but can't find more.
Thanks.

That formula describes the "lift-induced drag" for a planar wing. Lift-induced drag
As the definition implies, this drag is induced by the generated lift, the effect of stall (flow separation) is not contributing to this drag component.
Therefore, there is no other formula for the stalled regime.

Doesn't the epsilon in the formula above account for non-elliptical lift distributions? For all wings except those that create an elliptical lift distribution this value is going to be less than one, thus creating more induced drag.

Yes indeed, that's where it differs from the wikipedia version. I overlooked that part, I'll edit my answer. This doesn't change much about the content of the answer though.

Beyond the stall, the wing profile is governed by flat plate aerodynamics. The airfoil does still have lift and drag, and one could express one as a function of the other, but I have not seen a useful application of it.

Flat plate drag is a function of Reynolds number. The picture is from this document, and shows $C_D$ as function of $Re$ and AoA.
More info, an equation and 360 deg plots of a NACA 0012 profile in the answers to this question. Looks a lot like sine & cosine graphs, doesn't it.

If we interpret induced drag as the backward component of the lift vector (explained here and here), post stall is not much different from pre-stall.
It is simply the vector decomposition of the lift, so if we rotate the wing more, the induced angle of attack increases and induced drag increases.
However, with stall, when we rotate the wing more, we actually reduce the lift and thereby the induced drag.
The final experienced induced drag is influenced by both (i.e. how big is the lift force, and how much is it tilted backward), so how the induced drag actually develops with AoA depends on the relative change in both and thus is highly dependent on the airfoil.

From my understanding induced drag is the penalty for accelerating air (to create lift) and the creation of the wing tip vortices. If you deflect the air a lot it creates more induced drag, stronger vortices but also more lift and if you don't deflect it as much it creates less lift, less induced drag. Notice I haven't even mentioned the stall because to me that is a general cause and affect relationship. As you angle the airfoil up to create more lift you deflect the air down but this deflection of air also affects the incoming airflow (as long as we're subsonic) and because of that the net force vector starts pointing aft a little bit. It is this additional deflection of the force vector that causes a drag force, the induced drag.
Note: The lift after the stall doesn't drop to zero! There will always be quite a bit of lift throughout the full angle of attack range as can be seen in wind tunnel results (already linked by other users here but I'll repeat it: What is the performance of a flat plate wing?). Only at around 180° angle of attack and around 0° will the lift coefficient ever be close to zero and thus create no more induced drag. At 45° angle of attack the wind tunnel results show a lift coefficient of roughly 1.1, which can be more lift than if the airfoil is in normal operating range.


text:
What is the constant in this formula for additional lift?
Let’s consider the case of a plane flying s/l in a headwind with a positive gradient. A wing produces lift by inducing a bound vortex superimposed on the relative wind., and in the particular case of flying in a positive gradient, one can imagine an extra pseudo-vortex associated with the gradient itself, that re-inforces the bound vortex producing additional lift.
The question is now how to quantify that additional lift. From the variables that enter in the circulation theory of lift, one can guess that the variables involved are the density of the air rho, the airspeed v, the wing area A, the chord c and of course the wind gradient ß.
From dimensional analysis, it results that the extra lift L is:
L = k · rho · v · A · c · ß
where k is a constant to be determined. It can be probably done with a ‘material experiment’, but my question here is whether it can be derived from already known data or from a ‘mental experiment’.

See https://www.grc.nasa.gov/www/k-12/airplane/lifteq.html and https://www.grc.nasa.gov/www/k-12/airplane/liftco.html, describing some of the issues.

@xxavier, do you mean the angle of attack when you actually say gradient?

@GHB   No, of course I don't mean that... The gradient of the wind is the variation of wind speed with altitude. For example, if you have 20 m/s variation in an altitude difference of 100m, the gradient is 20/100 m/s/m = 0,2 s^-1

Why do you think that your formula is correct? There are a lot of unexplained assumptions in it. With the lift and drag equations of the first comment's link you should be able to get a formula using a physical model instead of guessing.

@Gypaets The variables are the relevant ones in the problem, in particular rho, v, A, and ß; with c added because of dimensional considerations. I have already found two possible solutions, one of them presumably exact (π/2) and the other is an approximate solution that differs by only 5%. But I'm not sure... Hence my question...

Could you explain the "dimensional considerations"? Wouldn't a formula like $L = k · rho · v^3 · A^2 / c^3 / ß$ fit too? This one probably doesn't make sense because $\beta$ is negative, but there is an infinite number of dimensionally correct formulas.

@Gypaets I agree... The 'dimensional argument' is not a definitive one. However, if you are able to derive an expression for the extra lift of a wing in a wind gradient, I would be very pleased to know your solution, since it would be an indirect answer to my question...

@xxavier I'll take a look at it if I have time. Perhaps you can find a formula searching for horizontal gust loads, there should be a lot of literature about it.

@Gypaets Thanks...!

The formula you have given looks strange to me, I have never seen it before. But possibly I can help you with the following brief explanation about kinematic relationships when flying under wind conditions.
Flight path velocity (VK) is the vector sum of aerodynamic velocity (VA) plus wind velocity (VW), see sketch. - When flying in a headwind condition aerodynamic velocity will increase and a pilot will need to decrease Alpha to keep the lift constant. It is the opposite way around in a tail wind condition. Now a pilot will have to increase Alpha in order to keep the lift constant and additionally will have to pay attention not to come too close to Alpha max. Or increase thrust.
If one uses the sketched kinematic relationships properly one does not need an additional formula for analysis.

If I understand all this correctly, this answer appears to solve for an instantaneous flightpath velocity solution dependent on an instantaneous wind velocity. However, I understand that the question is asking about a dynamic lift solution dependent on a dynamic wind gradient. I do not see how this answers the question and believe it would fit better as a comment. Once you have sufficient reputation you will be able to comment on any post.

@Cristoph  An aircraft flies always with respect to the mass of air., and doesn't 'feel' the wind for lift.  Lift is the same either in a 'headwind condition' or in a 'tailwind condition' because wind exists only in reference to a fixed frame, usually the ground.

@Jonathan Walters  Exactly...

Lift is not determined by the sum of wind and aircraft velocities (measured relatively to the ground). Only relative velocity of air (air velocity relatively to the aircraft). So there is no alpha change according to wind velocity relatively to the ground (what you name $V_w$), and neither change according to aircraft velocity relatively to the ground ($V_k$). Or maybe I don't understand your (untold) definitions of these velocities.


text:
For a given airfoil, with known Cl and Cd curves, how can I calculate the autorotation AoA range?
I'm trying to tabulate the differences of (vertical) autorotating behavior for rotors of equal chord and span, but with different airfoils. Of course, they can be studied case by case, but there may be a simpler, less laborious way... Hence my question...

This NACA report may help you further.
Basically, determine $v_i$ = the induced velocity in the hover, then vertical autorotation speed is around:

2 * $v_i$ for a rotor with 12 degree blade twist.
1.8 * $v_i$ for an untwisted rotor.

More detailed information in Prouty chapter 2, although the annoying non-metric constants pop up all the time.


text:
What's the effect of air density and temperature in the range of aspirated reciprocating-engine airplanes?
Reciprocating engines give more power with less revs when the aspirated air has a higher density. Wings also give the same lift at less airspeed when the air has a higher density. Drag is higher, too... And for any thermal engine, efficiency is higher the colder is the 'cold reservoir' (for an internal combustion engine, the outside air). What's the combined effect of these variables (density and temperature) in the airplane range if the engine is an aspirated ICE?

This seems a bit broad to me @xxavier.

@GdD I believe that something like the 'Breguet equation' may be derived, containing the variables density and temperature...  That's not so broad...

So you're asking for a mathematical formula? I have to admit I'm not sure what you're asking @xxavier.

@GdD Of course, a mathematical formula would be the best answer to my question, that –put in another form– may be: ¿Do you have a better range flying in a cold day than flying in a hot day (same air density)...? And, having an answer to that, what would be the influence of a different air density...?


text:
Is threshold crossing height and glide path angle the same for ALL airports and applied to ALL aircraft?
It seems to be agreed (at an international level) that these values are standard and should be respectively 50 ft and 3 degrees. Are all airports following these rules, and are they applied to all type of aircraft?
Why would departure operations not have the same kind of constraints?

The short answer is "no", especially for TCH.  (Long answer will come later today if nobody else gets it :)

LCY (London City) has an approach that is 5.5 degrees, and it used to be 7.5 degrees at one point in the past. I also know some short-field approaches if you are 50' over the threshold when crossing it, you are going to end up in the bushes at the end of the runway.

@UnrecognizedFallingObject, I will accept Gerry's answer, but your input is more than welcome! :)

@harveyAJ -- I'd just have restated what Gerry said

In the US, the requirements are specified in FAA Order 8260.3, United States Standard for Terminal Instrument Procedures (TERPS).
Section 2-3 states:

2-3. General PA Requirements. See Order 8260.19 for requirements
  related to GPA/TCH coincidence.
  a. GPA. Utilize a standard 3-degree
  GPA where possible. GPAs greater than 3 degrees but not more than the
  maximum (table 2-1) are authorized without approval when needed to
  provide obstacle clearance or to meet simultaneous parallel approach
  standards. Other cases or GPAs less than 3 degrees require Flight
  Standards or military authority approval (USAF not applicable).

b. TCH. The published TCH (nearest whole foot) should accommodate the
  largest aircraft height group normally expected to use the runway and
  must not be less than the minimum or exceed the maximum TCH.   Note:
  60 feet is the maximum TCH regardless of height group.
  (1) CAT I.
  The TCH is based on achieving an acceptable wheel crossing height
  (WCH). The WCH is the difference between the TCH and the approximate
  glidepath antenna-to-wheel height (see table 2-2).
  (a) The optimum
  TCH provides a 30-foot WCH. It must provide a WCH no less than 20 feet
  or greater than 50 feet.
  (b) Displaced Threshold Considerations. The
  TCH over a displaced threshold can result in a WCH of not less than 10
  feet if the height of the glide path over the beginning of the full
  strength runway pavement suitable for landing falls within the
  minimum/maximum TCH values.
  (2) CAT II/III. The optimum TCH is 55
  feet and must be between 50 and 60 feet regardless of height group.
    Note: To determine the
  minimum allowable TCH, add 20 feet to the glidepath-to-wheel height
  and to determine the maximum allowable TCH, add 50 feet to the
  glidepath-to-wheel height (not to exceed 60 feet).

So, the answer to the question is ; No, they are not all 3 degrees and 50 feet.

Additionally, many/most approaches do not match the 3.00 and 50 "rule" in actual practice.

Incredibly useful! Thanks A LOT for your input. @JonathanWalters what kind of tolerance is acceptable. are we talking +/- 10%, or more? Table 2.1 shows, for category A a max GPA of 6.4 -- which means that you literally double the touch down distance. Surprising.

It almost depends on the airport location(e.g. mountain area, city), in USSR most GTA were 2.40 degrees, and for military in ex-USSR countries they are still 2.40 dergees, because they use another ground facilities.


text:
Can an airport fine an aircraft for being too noisy?
I stumbled upon this article (sorry, in French!) stating that in order to avoid fines, Ryanair pilots start take-off procedures at the beginning of the runway (rather than at the "intersection"), with extra engine power (24klb instead of 22klb in Brussels airport) -> this allows pilots to take tighter turns and avoid the noise-sensitive Brussels region.
I know that most (if not all?) major airports have noise monitoring terminals (NMT) in their vicinity which constantly measure the noise as it is perceived on the ground.
From the article, it seems like a single aircraft can be fined for being too "noisy" (i.e. noise generated at monitor above a certain limit). If such is the case:

What is the noise fining policy around an airport / Are there internationally agreed rules on noise limits around airports?
Is it common practice (is it even possible) to "single out" an aircraft and fine the pilot/company for generating too much noise on ground?

Are you asking for a specific jurisdiction the answer may change at different place around the world.

@Dave I was interested in Brussels area jurisdiction in particular, but more generally it would be interesting to know whether an airport can fine a pilot/company for emitting too much noise at a given point where sound exposure is being monitored (I understand that limits may vary from one airport to another).

Ill answer this for the FAA (here in the US) but keep in mind this differs around the globe.
The FAA outlines some of their noise abatement information here. They created a special website that has a lot of the data here if you are interested.
There are 2 basic scenarios here in the US, towered and un-towered operations. There can be a noise abatement or related procedure in place in both cases and it is both the pilots and towers (when applicable) responsibility for knowing them and abiding by them. Some of them may be set in place by local governments (if its say a municipal airport) and you may face local legal action for violating them.
At a towered airport that has a noise abatement the tower will generally not vector you to that area or have you use a given runway provide conditions allow. For example when I fly out of KPNE there is an abatement in place, in this case they only list Rwy 15 arrival (stay above the glide slope) however there is another abatement in place on the weekends to keep you from flying over the heavily residential areas early in the morning. The tower vectors you appropriately for that one.

(source)
At un-towered airports there may be a published noise abatement that you are requested to follow. For example I fly out of KDYL which has a noise abatement in place (to keep you from flying over downtown). In this case we can see it noted in the AFD. Although its not fully explained the procedures are for RW 23 turn to 250 as soon as practically possible, for RW05 no turns under 1200 ft. and there are no touch and go's at any time.

(source)
In both cases the procedures have a similar outcome to what you have described, keep the airplanes away form the populated areas. The procedures vary heavily per airport and scenario but all generally strive for the same outcome.
The FAA advises you to first report a violation to the airport but also provides contact info for directly reporting to the FAA. You can single out a given aircraft by accurately reporting the time of the incident (and if its visible) describing the aircraft. Granted it can be difficult at an un-towered field to know who exactly was departing if no one was around to see it or on the radio to hear it. Once reported the local authorities may have the right to fine you for the violation (if that is the punishment on the books). For example in the NY/NJ area the Port Authority handles the violations and does hold the ability to issue fines.
Long beach airport lists their fines on their site

If a plane violates the Noise Ordinance, how much are they fined?

The initial phases of our violation process are educational: the first
  time an owner/operator violates, they will receive a complete packet
  including a copy of our Noise Ordinance, an outline of what the
  infraction was, a letter from GANC offering assistance with
  procedures, and a warning letter asking them to contact noise
  abatement staff.
The second violation involves a notification letter
  of infraction and a request for a written noise abatement program,
  where we ask the owner/operator to communicate how they plan to
  operate without violating our ordinance in the future.
The third violation is a fine of $100 dollars. The fourth and every subsequent fine of 300 dollars. Please note that Military aircraft
  are exempt from this policy.

And it looks like, according to the regulations, the airport manager issues the fine and the payments go to the airport. This may vary by jurisdiction on how they chose to govern things like this. Over all the answer to your question is, yes airports can fine pilots (well really owner/operators) for noise violations.
There are also noise limits on aircraft that deal with engine noise but are generally handled during the certification phase of the air frame. This helps to reduce airport noise overall.

As for global regulations the IATA has outlined some stuff here with the full text here. ICAO has a set of policies you can find some references to here.

Individual airports can also ban aircraft from using them if they violate their noise requirements (like Santa Monica).

Thanks @Notts90 for pointing that out and thanks Dave for updating! I'm impressed by the level of detail! Will need a couple of hours to go through all that :)

I will add a bit of extra info, in case people are interested in noise fining policiy in the UK (Heathrow airport). Stumbled upon this: http://your.heathrow.com/heathrow-departure-routes-explained/ there is a table explaining the fine policy at Heathrow airport in the UK (scroll down to section "Noise limits on departure"). The table details (for departures only) the different penalties applied for aircraft that go above noise exposure limits

In the EU, regulation differ from airport to airport. However, every major airport use a system which logs every radar track from every movement around the airport. Every airplane can by using the radar logs be "singled out". A movement is defined as either an approach or a departure.
If someone complains about aircraft noise and provides a time for the inconvenience the airport can always go in and see which aircraft individual that caused the noise. All movements/tracks is usually controlled on a regular basis. If the pilot/airline has broken any of the environmental conditions the following will happen:
A polite letter is sent to the owner/airline of the aircraft telling them that they have violated a condition in the environmental permit, how, where and when. If multiple violations from the same airline occurs the airport manager contacts the airline management. Usually it stops there. Otherwise it will end up in court.
In Sweden where I come from the airport manager is responsible to make sure that the conditions in the environmental permit is fulfilled - not the aircraft owners. The regulating authorities can issue a fine to the airport if multiple violations occurs, not to airlines or pilots.
However, by using the airport you must as a pilot agree to follow the designated routes for approach and departure. By following the routes (SID, STAR) and the instructions from the ATC the aircraft will not violate any environmental condition. If the pilot cannot follow SID, STAR and ATC instruction the pilot will end up lose the license to fly.
EDIT: Some (I would guess all) airports have fines on noisier aircraft models, based on the ICAO noise certification value that exist for every aircraft model. That has nothing to do with fines from pilot errors (turn to early or to late) that also causes noise over certain areas, that can be no-fly-zones.

How do you work out whether an aircraft has breached the law from radar data only? Sure, the altitude clearly has an incidence on noise, but I guess you need to have a look into power-setting which is not part of radar data (or is it?).... I guess my question is, how can you be sure the aircraft has broken the environmental conditions when the airport isn't equipped with noise monitors? (I am aware that I just split hairs here :))

How would they use radar to single out no-transponder targets (given that primary radar returns are reliably intermittent and reliably vague about an aircraft's precise position)?


text:
In a gyroplane, how can the angle of attack of the rotor disk be calculated?
In a gyroplane, how can the angle of attack of the rotor disk be calculated as a function of the relevant variables?
Those 'relevant variables' are the rotor's angular velocity, the aircraft's airspeed, the blade chord and pitch, the rotor diameter, the slopes of the drag and lift at the relevant intervals of the blade profile and the air density...

Don't forget the attitude of the gyrocopter!

The attitude of the gyro's body has nothing to do with the AoA of the rotor tip-path plane, when the gyro's flying s/l, since that angle is determined only by the rotor's drag and lift.


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To which side did the first Cierva autogyros fall?
The first Cierva autogyros, before the introduction of the flapping articulation, fell to the right when the take-off was attempted, according to witnesses. That had an explanation, as the rotor turned clockwise (seen from above) so that, when the aircraft moved forward at a certain speed, the right-side blades lost lift, the left-side blades gained lift, and the resultant torque rolled the autogyro to the right...
But, why didn't gyroscopic precession shift the reaction by 90º, pitching the nose up so that the machine fell backwards...?

Dissymmetry of lift

@Ron Beyer Dissymmetry of lift produces forces that caused the first autogyros, fitted with rigid, non-flapping blades to... roll to one side?  or to pitch up, due to gyroscopic precession...? That's the question.


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Could floppy rotor blades be usable?
Autogyro and helicopter blades are more or less flexible, and when not stiffened by centrifugal force they droop noticeably. A extreme case would be that of fabric blades. They have been used at least once, as propeller blades in the airship ‘Parseval’.
Could fabric blades work as rotor blades of an autogyro?

Do you mean a blade with no spar that just flops down like an old sock when not spinning?

Yes... Like the non-spinning blades in the left picture...

Many (if not all) "first flights" helicopter and De la Cierva's autogyros had for sure fabric-covered blades.

@sophit. Yes, but one thing is a rigid structure with a fabric covering (like many wings, fixed or rotating), and another very different is a completely 'floppy' blade, stiffened only by centrifugal force...

Then I don't think so since it would miss any torsional stiffness. Plus you need some ribs anyway in order to give an airfoil shape to the blade chordwise. But I agree that spanwise you wouldn't need any particular structure (if the fibers of the fabric has a proper layout to resist the centrifugal force); but then you couldn't change the pitch of the blade.

@sophit. No problem with the pitch... Some autogyros of the 30s did have variable pitch, but that was exceptional. Most historic autogyros were fitted with a fixed-pitch rotor, as well as almost all of present-day ones...

More than the missing pitch control, the missing torsional stiffness would be a paramount problem. Due to the aerodynamic environment typical of rotating wings, the blade would be torqued with different intensity along its span and in a oscillating manner. With no proper structure supporting this movement, the blade would flap in torsion just like a flag.

I think you would need more than 26 floppies, so you would run out of drive letters.

For thrust to pull on the hub, a propeller blade must be able to transfer shear loads from the circumference to the center. Add a bending moment when the distance between the circumference and the hub becomes nonzero. This requires a stiff propeller.
With flexible blades thrust can be achieved when the blades form a cone from the lift force pulling them forward. This will be added to the tension created by the centrifugal force on the blades. From the right picture it seems that no such lift was achieved when the picture was taken.
However, the Parseval dirigibles could achieve speeds above 40 km/h, so the caption "… UND IN FAHRT" (… and in motion) is not quite correct. The complex hub arrangement actually allowed to change blade pitch and even to reverse pitch in flight.

Austrian military dirigible M1 (picture source), a Parseval-type dirigible built in 1909.
Now to your question:

Could fabric blades work as rotor blades of an autogyro?

Maybe, when spun up before take-off. A typical autogiro does not need to power its rotor directly because it is set in motion by the airflow. Later Cierva autogiros did power the rotor in order to shorten their takeoff distance. Once in flight, all power is used to spin the propeller because driving the rotor would create undesirable torque which needs to be counteracted either by a second rotor spinning in opposite direction or by a tail rotor like in Sikorsky-type helicopters.
It is important to keep the blades at a positive angle of attack so they will constantly produce enough lift to keep the autogiro afloat. While it seems that changing the attachment points of the two ropes which formed the leading and trailing edges of the propeller blades was enough for the Parseval propeller, the much higher aspect ratio of a typical autogiro blade will most likely restrict lift production to the blade section close to the root. Since a flat plate is indifferent to pitch changes, the pitch angle of such a blade would be only controlled by the tension in the ropes from the centrifugal force. This could work but I would rather use a stiff blade to make sure that their angle of attack is well controlled.
Also, a good airfoil will increase the range of possible angles of attack with good efficiency which is especially helpful for helicopters. Using a flat plate airfoil will definitely cost performance.


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How can the effect of wind gradient in a glide be calculated?
If an airplane glides in a mass of air where the headwind changes with altitude, it seems logical to think that the length of the glide –as measured by a ground-based observer– will be longer in the case of the headwind decreasing with altitude. The reverse should be true in the case of the headwind increasing with altitude...
How could a mathematical expression for that glide be derived...?

I assume you want to assume that the pilot is manipulating the controls in such a way that the actual airspeed is always exactly equal to the airspeed that would yield best glide angle over the ground in a uniform airmass (no gradient) that was moving at the wind speed that the aircraft is currently experiencing at that instant?  So descending with a headwind with a normal gradient, the pilot is actually decreasing the airspeed?  (This would be a logical way to operate the controls and I think it is the optimal way at least in the case where no course changes are allowed.)

Or do you want to just assume constant airspeed?

Obviously if course changes are allowed then the problem is much more complex-- the albatross can obtain an infinite glide ratio over the long run in such a scenario, using dynamic soaring techniques

@quietflyer The criterion could be that of manipulating the controls in such a way as to maximize the energy extraction from the wind gradient...

This may take some time -- but it certainly should be answerable

You have your descent rate in feet per minute, based on IAS, your aircraft, and the existing conditions (altitude, temperature, pitch, etc).  At one altitude with that IAS (and a conversion to TAS, if you're so inclined) and the winds there, you have a particular (calculable) groundspeed. So you can calculate that in each minute, you travel "this" far forward, and you lose "this" much altitude. So you can compute your descent gradient.
Passing a new altitude with different winds, your groundspeed (and, upstream of that in the calculations, your TAS) is now different, and so your forward travel per minute is different, and you have the new gradient.
That's the "slices of the cucumber" method; if you want to do a full integration to get a smooth curve (assuming that your wind data is amenable to that sort of an approach), well, you're into more math than I can recall from school days.
The other dynamic that this approach won't capture is that as you descend into an increasing headwind, you will gain IAS as the inertia of the aircraft doesn't change as quickly as the velocity of the air can change.  This effect doesn't matter much if the change in wind speed is small or gradual, but descending from 100 knots of tailwind at cruise down to 20 knots at low altitude, it matters -- you've gained energy that needs to be accounted for (and dissipated) if you're planning to cross a given fix at a specified altitude & airspeed.  Unfortunately, the 737 FMC (and probably many others) doesn't account for this effect; it only knows that your groundspeed will change with altitude.

I think the whole point of the question is surely to account for the energy actually extracted from the wind gradient, taking into account the aircraft's inertia-- i.e. the answer should not be the same for a light weight balsa glider than for a heavy massive glider even if they happen to have the same glide ratio at any given speed of interest.

@quietflyer  Since the FMC designers don't worry about that energy gain, my initial thought was the more basic math of just the gradient itself, which is what the question mentions.  Adding to that the math to account for gained/lost energy, and/or adjusting airspeed to accomplish particular goals (i.e. your comments on the OP), would have to be added on top of that basic computation.


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How do diffusers turn velocity into pressure?
There are many resources that give explanations for the behavior of nozzles and diffusers. But at the crux point they all say, "Velocity goes down and pressure goes up." As if that doesn't warrant any deeper explanation, or as if it were just a law of nature.
To me, the reason behind this energy transfer isn't obvious.
To maintain a constant mass flow rate, $\dot{m}=const$ , through a small inlet and a large outlet you would need a deceleration of the flow. To decelerate a flow requires a force, $F=ma$. Forces interactions are equal and opposite so the fluid would exert a larger force, relative to the inlet, if forced to slow down. But what is the origin of this decelerating force? Why does this geometry increase the $\frac{F}{A}$ of the molecules that pass through it? I understand the energy conservation, but how is this behavior explained in terms of force interactions?
It's like you asked how an electric motor worked and someone said, "By turning electric energy into rotational motion." and you said, "How?" And they just repeat, "By turning electric energy into rotational motion." Energy balance just isn't descriptive enough.

It may sound counterintuitive but increasing the speed of a fluid reduces the pressure. better explication on physics.SE: Relation between pressure, velocity and area

Warning N°1:
I'll avoid energy conservation, but cannot set aside mass conservation obviously.
Warning N°2:
Both speed and pressure settle in a way that abides the laws of physics. It's not like one settles first, then the second follows. Don't let my wording fool you.
Warning N°3:
I won't consider temperature in addition to speed, density and pressure. It's too much for an explanation.

There are many, many ways of seing this.
The wrong but easy answer
People who 'simply' say:

Velocity goes down and pressure goes up.

Are, often, wrong. This only holds in perfect, incompressible, irrotational flows and is known as Bernouilli's principle. If my (French!) aerodynamics teacher heard anyone mention it, that person would probably lose points! These conditions are often far from reality so the consequences don't hold every time. However it can be used as a guideline to get a gut feeling about a low-Mach flow.
(Note in locally supersonic flows, the exact opposite might apply, so this warning is legit!)
Energy
The easiest answer is energy conservation. You mentioned you wanted another:

I understand the energy conservation

So I'll pass.
Forces
Your nozzle is a convergent manifold, your diffuser is divergent. One acts exactly opposite to the other (just reverse the time in steady flow) so I'll address convergent axisymmetric shallow nozzles. Shallowness means speed is quasi-axial everywhere.
Furthermore, in aviation we are concerned with planes, so I'll assume the intake velocity is constrained and cannot go down.
Let's get to equilibrium first.
Now try to cram a still fluid through a restricting pipe. It won't like it, and will resist (inertia, plus the surface pressure of the nozzle's axial component, etc. see? Forces!), thereby increasing its pressure. This pressure increase will propagate to the whole intake and raise that pressure. And now the intake has everything it needs to push the whole fluid forward:

high intake pressure P0
constrained intake speed V0

So the fluid effectively moves through the pipe.
How to describe the equilibrium
First off, any radial section of fluid has quasi-uniform pressure, otherwise the fluid would pick up a large radial speed, so we would not be at equilibrium yet.
Next, apply conservation of mass. It forces conservation flow throughout any section of fluid with A×V×rho=Cte. If frontal area is restricted, then either or both speed and density must increase. The amount by which each increases depend on the fluid's properties (compressibility etc). So here you go: speed must increase in the convergent nozzle. Also as a by-product, density may increase.
How does that happen?
Simply, a force must push the fluid.  Remember the intake has very high pressure necessary to maintain steady-flow? Well that pressure is propelling the fluid (and there must be a low pressure at the tighter end (exit) as well).
If we do a static analysis of a thin section of fluid, it has low speed behind, high speed in front, so each molecule is accelerating. The section behind provides high pressure, that pressure translates into an axial force, the molecules accelerate. The section in front has lower pressure, and doesn't push back as much. That pushing-forward-hard/not-pushing-back-as-much is the pressure differential.
So along the flow, we should see the pressure decreases.

There you go, I've used:

steady-flow assumption
conservation of mass
second law of Newton

Look Ma, no energy!
P.S sorry if I sound like I talk to a 5 y.o. !

don't be sorry for providing an understandable explanation. If it sound like you talk to a 5y.o. and if you are accurate, it looks like you achieve to formulate a good explanation.

While we wait for a probably better answer, here's my tentative.
You state that you understand the concept of constant mass flow. Let's for a moment write the mass flow properly:
$$\dot{m} = \rho A v$$
on the left we have the mass flow $\dot{m}$, on the right we have the density $\rho$, the area $A$, and the velocity $v$.
If we want $\dot{m}$ to be constant while changing $A$, we need to change $\rho$ and $v$ accordingly. In these scenarios $\rho$ is taken as roughly constant, leaving only the velocity as free variable. While this might be more true for liquids, it is not too far from the reality also when air is involved (although you might observe minor variations in density).
Where do the forces come from? The walls of the duct and the fluid downstream (when decelerating, the fluid that is already at a slower speed will effectively work as a "wall" for the incoming fluid) or the fluid upstream (when accelerating the incoming fluid will push the rest of the fluid like an extruding piston).
In other terms the required energy comes from the pressure differential (the faster fluid has lower pressure).


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How does the training for an EASA license from the US compare to that from Europe?
My plan is to work as a commercial pilot in Europe. But, I heard that the training in Europe might be more expensive and harder than in the US.
For example, to get your PPL you have to face some 1000 theoretical questions before even getting on the plane.
A friend of mine who got his licenses in the US told me that there are academies that offer EASA licenses but in a more affordable and "inviting" kind of training.
Is applying for EASA licenses in the US really a better option? (Cost and training.)

Who told you you need to answer 1000 theoretical questions before starting flight training? That sounds completely made up

Even if your friend is right about the 1000 questions, the requirements for an EASA license don't change based on where you do it. Having said that, flying in the US is indeed much cheaper than in Europe.

You definitely do not need to answer any theoretical questions before beginning flight training in Europe. In fact pop down to your nearest airfield, find a flight school, and chances are they will get you in the air (even for a trial flight) as soon as they are able.
Whoever told you that may have been thinking of the examinations you need to pass to get your PPL, and while 1000 questions is probably a high estimate, you need to be able to answer exam questions on a bunch of subjects such as Meterology, Air Law, Human factors and radiotelephony. You do this during your flight training, but again there is none of them you need to pass before you can begin.
I am from the UK, and I learned to fly in California. It was before the EASA licenses (In those days they were JAR licenses) but the idea was the same - I was training in the US for a license that was valid in Europe. I had to do the same training, and take the same exams as if I was in Europe learning  there was no difference.
On the cost, yes it was slightly cheaper per hour in the US however when you factored in getting there, staying in accommodation and food etc I don't think there was really that much in it. It was more an opportunity (excuse!) to take a 4 week holiday and do nothing but fly every day in great weather (Something which in the UK, at least, is hard to get to do).
Fun fact: I did this 11th October 2001. Conversation at LAX with TSA having explained I'm entering the US as a lone male to learn to fly - "Don't worry Mr C, you don't fit the demographic we're currently looking for".

As you said, the weather is a massive benefit of some US locations. Learning to fly in many European countries, expect a lot of cancelled lessons for bad weather/lack of visual conditions. And of course having a compressed course means you can concentrate fully on the curiculum and not have to spread it out over months or years of a few hours a week.

@jwenting exactly. It could take a couple years to get to 40 hrs in the UK if you fly every few weeks (what with cancelled lessons due to the dreaded weather). It was easy to get to 40 hrs in 4 weeks in SoCal.

And to make things more expensive, that extra time also means a lot more refresher lessons on theory as well as more time per flight needed to get reacquainted with aircraft and procedures.

But, the counter argument, was that having returned from SoCal with my PPL, I needed about 10 more hours of instruction in the UK. It's a lot harder to navigate without giant mountains one side,the Pacific the other, and giant highways leading between sparse settlements. Turns out, every green field in the UK looks like the next, and settlements are a little harder to distinguish from one another!

yup, But that's not related to EASA but to area familiarisation and would apply to say a Spanish person moving to the UK as well.


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Is it allowed to mount fake missiles on a civilian aircraft?
In this answer to a question asking to identify an aircraft, we can see a picture of a Aero L-39 Albatros with some missiles hanging from the wings:

(flickr.com) N915WE.
Supposedly, this is a civilian airplane, and another user pointed out the oddity in a comment. The author of the answer then replied that [those missiles] "are as real as this being a USAF L-39 ;)". This second picture shows an airplane with "United States Air Force" painted on it.
Does this mean that it is perfectly legal for a civilian aircraft to mount some fake missiles? And to write "USAF" on an airplane that doesn't belong to the USAF, even? Especially considering this airplane can really be configured as a military one, with real missiles!
To me this looks like going through security checks at the airport with a fake gun in your hands. Sure, it's fake and it can't harm anyone, but I'm not sure the police would appreciate my sense of humour.
Seriously, is this allowed? With all the attention to security (which often borders on paranoia), it is allowed to fly around with fake missiles? Won't this lead to unnecessary confusion, fear, and even false alarms?

Are you asking about US regulations?

@Pondlife I actually thought there would be worldwide regulations about these matters, but your question makes me realise it's a naive expectation. If a single answer about all the world isn't possible, I'd stick with the US, since this is where the picture was taken. And if the question doesn't become too broad I'd also like to know something about Europe.

The Textron LandAir Scorpion, built by Cessna, has performed test flights with "fake" armaments as well as demonstrated ability to fire live armaments.


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What does a fuselage frame structure of a non-pressurized transport aircraft look like?
What does a fuselage structure of a non-pressurized transport aircraft look like? I can find loads of examples for pressurized fuselages, but almost nothing for non-pressurized ones. The DHC-5 Buffalo comes to mind, but I can't tell how the fuselage frame is made, e.g.- how the I-beams in the floor are laid out, etc.

Search "cutaway" to find images similar to this.

Unpressurised structures are very different from each other, because they are optimised for different features and the restrictions  due to pressurisation are not there.

A pressurized aircraft structure differs from non-pressurised in that the fuselage center area, including the cabin and baggage compartments, are built as a pressure vessel.
Except for:

strengthened frame and windows
forward and aft pressure bulkheads
pressurization systems

the aircraft structure and design not related to the pressure vessel (like the floor) remain unchanged.
There are many examples of non-transport civil aircraft that have pressurised and non-pressurized versions.  For example, a Beechcraft "P-Baron" or a Cessna P210 Pressurized Centurion has smaller windows and different cabin doors you can easily observe.  Yet, the design principles of the aircraft structure, besides beefing up the pressurized areas remain the same.
Most non-pressurized transport aircraft are utility or military in nature, as is the DeHavilland aircraft you mentioned.  Design considerations for these aircraft, like the floor you mentioned, are related to their mission, not pressurization.  That is, unless the floor itself is a pressure vessel wall.

The biggest difference is in the cross section. Pressurization leads to a round cross section which is less practical and harder to build than a boxy cross section. Also, pressurization means stressed-skin while non-pressurized structures can be a canvas-covered steel tube frame.


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Iris Precursor - 4D Air Traffic Control System
I just read this article . From the article at the very end -

ESA claims that the new tech, which may eventually require an Iris
  terminal/transponder to be attached to every plane in European
  airspace, provides "4D" flightpath control. Prosaically, this means it
  provides four coordinates, locating each aircraft according to
  latitude, longitude, altitude, and time—which ESA says "will enable
  precise tracking of flights and more efficient management of traffic."

While it would be known in time whether it truly works as advertised or needs kinks to be worked out, something like this should have made events like 'disappearances of MH370' much more rarer as rescuers would have much more precise locations to search in case of any untoward incident.
The simplest way to think of it is like the radio and Uber cabs which constantly ping back to the home location so they know where the drivers are at all times. Just an expansion of the idea at a somewhat ridiculous height :)
Do people think it should improve the safety of the aircraft or it would be another tech. that is just as liable to fail as others ? Hopefully people keep an eye on this technology and where it goes. If anybody knows any similar technology, feel free to share as well.

MH370 probably had this technology or similar tracking technology on board. The problem is that the pilot can pretty easily turn it off... Basically in the United States, this is what is going to be implemented with the ADS-B and NexGen mandate in 2020, although most commercial traffic already comply.

Your Uber analogy is a bit flawed, since aircraft already have all sorts of tracking devices (technically referred to as surveillance equipment). New ATM systems that use 4D trajectory calculations do not so much gather new information, they mainly use and process the information in a different way compared to conventional systems.

Your question is not clear.  Are you asking about Iris specifically or "constantly ping back location"?  This system would have done absolutely zero to stop MH370 crashing into the sea with the loss of all souls onboard.

@J.Hougaard What are ATM systems ?

ATM - Air Traffic Management

@Simon You misunderstood me, what I am referring is the after search of 'where is MH 370' .  If such technology was there (and not turned off) it's possible we would have known if some hostile action (hijack, shot down by rocket etc.) or something else (like in Apollo 13 after incident analysis) . As of date, we know nothing why MH370 failed and all is pure speculation.

All of which is addressed in the answers to the duplicate question.  It would not have saved the people onboard and it is very speculative that anything will be learned in the future.  Have a read of the answers provided.

As far as I understand your idea, you missed one point: Tracking (usually) needs a signal to be sent by the aircraft, which is not a problem, they do it already, many signals. But the signal must be received by a station in range. While this is not a problem over land, it's indeed a problem over water unless you use a satellite as the receiving station. This was not the case for MH370 because this as a cost and is not mandatory. But this is going to be mandatory soon as part of the modernization of ATC. Is Uber capable of tracking over water? No because they use the mobile telephone service.

True, got your point, the analogy was there to make it understood. I wasn't saying it was a cent percent the real deal :)

Is Uber capable of tracking over water? - Not yet...


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Are there any airports which use a metro to transport cargo?
Many airports around the world are increasingly being joined by Metro conveniencing people. Majorly, it is people who probably will use the metro. I do have a sneaking suspicion that the metro would also be a pretty inexpensive good carrier. Two things which I think work in its favor -
a. Security on Airport Metros is higher so that much less hassle.
b. Most of these Metros run on specific times so it's easier as it's consistent.
Are there any airports that people know that transport air cargo via metros after being bought by Aircraft ?

How do you define metro? Do you simply mean an underground train?

Interesting question.  A metro could carry only a small amount of cargo, though.  Why not just install a spur line to allow a rail carrier access to the airport?  Economies of scale snd all...

metro, for e.g. https://www.mmrcl.com/map/ click Airports and you'll see what I mean. This is few years away, and Delhi Metro Express Line http://www.delhimetrorail.com/Airport-Express-Line.aspx which is already operational.

@acpilot - could you share what you mean by spur line ? Could you elaborate a bit please. I haven't heard that term before.

A spur line is an offshoot of an existing main line.

Metros are commonly used to transport cargo between airports.

@JonathanWalters I think we differ on what we mean by Metros :(

@shirish Sorry, it was a joke ;)

ah...ok, didn't get it :(

DFW Airport's original train system had cars built to carry mail and luggage.  Most of the system was never used because it was slow, and there were worries that it was hard to train employees to interface with it. I would guess that a lot of airports have not tried such as system because their trans are optimized for passengers, so it is faster to just move luggage across the tarmac on trucks.
Edit: Jonathan Walters mentioned that Denver also had a system, but it was buggy so they stopped using it.

Welcome to aviation.SE! Do you have any sources about this?

Best I can get you is this Wikipedia article. The citations seems to be old, so I cannot completely verify them, but there are a few photos of the system, so I tend to believe it. As for the last part, about the system, I simply am making an educated guess.

You can add Denver International. Designed to use baggage carts on rails, but had many problems, never fully implemented, decommissioned in 2005

It's still not clear from the question but I think it's asking about a train to and from the airport, not within the airport.

Few months back, I visited India and landed at their Indira Gandhi International Airport. During my exit, I was about to take the cab to my hotel but then I found their Airport Express Line. So they had this metro service for their passengers and it connects to major parts of New Delhi.
Later during my stay there, I found out that Airport metro had a bit higher fare than their local metro. But the services and the kind of security they provide was great. Passengers before boarding Airport metro can give their luggage at the time of boarding the train and then no need take tension at the airport. I do not know if they transport air cargo or not but if they are transporting passengers luggage they might transport air cargo.
Here I found a link which explains that they will start cargo service on their Airport Express Line.


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All Electric Jets
I've been researching electric jets, and I have seen a number of schemes. What is the most likely way to build an all-electric jet engine, assuming that the power source is available and practical?

Since there is no fuel to burn, it's not a "jet engine", but a ducted fan. Unless you are asking about compressing the air and using its expansion to produce propulsion?

"Assuming that the power source is available and practical"; that's a very big assumption, at least today. See also this question, and this one.

Well I suppose one COULD design a brayton cycle gas turbine which uses heat introduced into the gas stream by electrical energy, either in the form of resistive heating elements or high voltage arc flash.  Fairly impractical considering that - and especially for a high bypass turbofan engine - it would make more sense to just use a ducted fan driven by an electric motor.
So I guess the real question here is not could you design an electric jet engine, but rather, why would you want to?
If you are expecting efficiency improvements, especially a more exergetically efficient engine, an electric jet makes no sense.  An electrically powered ducted fan engine is more practical.
Again we have had this discussion multiple times on this board about the feasibility of large electric aircraft but it always comes down to a problem of energy density in the power source which makes such designs impractical.